The problems associated with traditional energy sources, such as coal, oil, nuclear energy, and non-renewable energy, have long been noted, including causing serious environmental concerns as well as their limited supply. A solution to these problems is the development and use of alternative energy sources, such as wind, solar, and water. Wind has been seen as a viable energy source, as wind generally exist in all environments, while solar and water supplies may be limited in certain environments. Thus, wind turbines have been developed to harness wind as an energy source; however, disadvantages and inefficiencies with wind turbines still exist.
A common commercial wind turbine that exists today is the horizontal axis wind turbine that utilizes large blades that rotate about the horizontal axis. In order to be efficient, these wind turbines must be mounted high in the air thereby requiring high towers and long blades which are difficult and expensive to transport. Because of their height, these wind turbines are also difficult to maintain since the gearbox, generator, and rotor are all located at the top of the tower. In addition, the cantilevered loads and the associated vibration effectively over-heat and prematurely wear the rotational bearings thereby causing early expiration of the bearings.
To cure some of the problems and disadvantages associated with horizontal axis wind turbines, vertical wind axis turbines were developed. One commonly known vertical axis wind turbine is the Savonius-type wind turbine which is simple in concept and construction and is utilized to convert the force of the wind into torque. The principle involved in the Savonius-type wind turbine includes the wind striking an object, wherein the kinetic energy of the wind is transferred to affect the object by either forcing the object to resist the force of the wind (in the case of a building) or causing the kinetic energy of the wind to move the object (sailboats, etc.).
Certain Savonius-type wind turbine designs capture the energy of the wind by using semicircular vanes that are offset from the center of rotation of the wind turbine. The result is that the wind energy is converted into torque about the center of rotation of the wind turbine. The Savonius-type wind turbine operates on the principle of drag differential from one side of the wind turbine to the other. The drag differential creates a high drag side that is powered by the interaction of the kinetic energy of the wind striking the vane such that energy is transferred to and power is absorbed in the wind turbine. The opposite side of the wind turbine is a low drag side or a recovery side, which presents a lower drag profile as the wind turbine travels into the incoming wind, and thus, the wind turbine absorbs less energy. These differences provide a drag differential and an energy absorption differential that results in a torque that causes rotation of the wind turbine about a rotational axis or shaft.
This Savonius-type semicircular vane design has proven to be functional. However, the amount of torque the semicircular vane design can produce is limited by the length of the lever arm (the distance from the center of rotation to the center of pressure absorption) and the amount of drag differential caused by the shape of the front and the rear of the vanes. The amount of torque created is also limited by the velocity of the wind, as the Savonius-type wind turbine is a drag type object not an airfoil. The vanes of the Savonius-type wind turbine can only spin at the same speed or a lower speed than the wind speed and not faster than the wind speed, such as in an airfoil application.
It would be desirable to create a Savonius-type wind turbine that is more efficient than conventional Savonius-type wind turbines by increasing the drag differential between opposite sides of the wind turbine to increase the amount of torque generated.